U.S. patent application number 11/467062 was filed with the patent office on 2008-01-03 for apparatus for monitoring electron density and electron temperature of plasma and method thereof.
This patent application is currently assigned to KOREA RESEARCH INSTITUTE OF STANDARDS AND SCIENCE. Invention is credited to Jung Hyung Kim, Dae Jin Seong, Ju Young Yun.
Application Number | 20080000585 11/467062 |
Document ID | / |
Family ID | 38875367 |
Filed Date | 2008-01-03 |
United States Patent
Application |
20080000585 |
Kind Code |
A1 |
Kim; Jung Hyung ; et
al. |
January 3, 2008 |
APPARATUS FOR MONITORING ELECTRON DENSITY AND ELECTRON TEMPERATURE
OF PLASMA AND METHOD THEREOF
Abstract
The present invention relates to an apparatus and method for
monitoring an electron density and electron temperature of a
plasma. The apparatus includes an electromagnetic wave generator
that continuously transmits electromagnetic wave of a series of
frequency bands, an electromagnetic wave transceiver connected to a
plasma within a reaction container and electrically connected to
the electromagnetic wave generator so that a frequency of the
transmitted electromagnetic wave is correlated to the electron
density and electron temperature of the plasma, the electromagnetic
wave transceiver transmitting the electromagnetic wave, a frequency
analyzer electrically connected to the electromagnetic wave
transceiver, for analyzing the frequency of the electromagnetic
wave received from the electromagnetic wave transceivers and a
computer electrically connected to the electromagnetic wave
generator and the frequency analyzer, for calculating a correlation
between the electron density and electron temperature, and a
corresponding electromagnetic wave based on a frequency band-based
transmission command of the electromagnetic wave and the analyzed
data.
Inventors: |
Kim; Jung Hyung; (Daejeon,
KR) ; Yun; Ju Young; (Daejeon, KR) ; Seong;
Dae Jin; (Chungcheongnam-do, KR) |
Correspondence
Address: |
ALLEN, DYER, DOPPELT, MILBRATH & GILCHRIST P.A.
1401 CITRUS CENTER 255 SOUTH ORANGE AVENUE, P.O. BOX 3791
ORLANDO
FL
32802-3791
US
|
Assignee: |
KOREA RESEARCH INSTITUTE OF
STANDARDS AND SCIENCE
Daejeon
KR
|
Family ID: |
38875367 |
Appl. No.: |
11/467062 |
Filed: |
August 24, 2006 |
Current U.S.
Class: |
156/345.48 |
Current CPC
Class: |
H05H 1/0062
20130101 |
Class at
Publication: |
156/345.48 |
International
Class: |
C23F 1/00 20060101
C23F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2006 |
KR |
10-2006-0061055 |
Claims
1. An apparatus for monitoring an electron density and electron
temperature of a plasma, comprising: an electromagnetic wave
generator that continuously transmits electromagnetic wave of a
series of frequency bands; an electromagnetic wave transceiver
connected to a plasma within a reaction container and electrically
connected to the electromagnetic wave generator so that a frequency
of the transmitted electromagnetic wave is correlated to the
electron density and electron temperature of the plasma, the
electromagnetic wave transceiver transmitting the electromagnetic
wave; a frequency analyzer electrically connected to the
electromagnetic wave transceiver, for analyzing the frequency of
the electromagnetic wave received from the electromagnetic wave
transceiver; and a computer electrically connected to the
electromagnetic wave generator and the frequency analyzer, for
calculating a correlation between the electron density and electron
temperature, and a corresponding electromagnetic wave based on a
frequency band-based transmission command of the electromagnetic
wave and the analyzed data.
2. The apparatus as claimed in claim 1, wherein the electromagnetic
wave transceiver comprises: first and second coaxial cables that
are electrically connected to the electromagnetic wave generator
and the frequency analyzer, respectively, and are disposed in
parallel; and a transmit antenna and a receive antenna that are
connected to and projected from one ends of the first and second
coaxial cables, respectively, on the same axial line and are
connected to the plasma in order to transmit and receive the
electromagnetic wave.
3. The apparatus as claimed in claim 2, wherein each of the first
and second coaxial cables comprises a dielectric-coated layer
coated/shielded at a predetermined thickness.
4. The apparatus as claimed in claim 1, further comprising a
conveyer connected to the other end of the electromagnetic wave
transceiver, for causing the electromagnetic wave transceiver to be
selectively conveyed within the reaction container.
5. The apparatus as claimed in claim 4, wherein the conveyer is
driven by a stepping motor.
6. The apparatus as claimed in claim 5, wherein the electromagnetic
wave transceiver is disposed along a radial direction of the
reaction container.
7. The apparatus as claimed in claim 6, wherein the conveyer is
driven by an oil-pressure cylinder.
8. The apparatus as claimed in claim 7, wherein the electromagnetic
wave transceiver is disposed along a radial direction of the
reaction container.
9. A method of monitoring an electron density and electron
temperature of a plasma using an apparatus including an
electromagnetic wave generator that continuously transmits
electromagnetic wave of a series of frequency bands; an
electromagnetic wave transceiver connected to a plasma within a
reaction container and electrically connected to the
electromagnetic wave generator so that a frequency of the
transmitted electromagnetic wave is correlated to the electron
density and electron temperature of the plasma, the electromagnetic
wave transceiver transmitting the electromagnetic wave; a frequency
analyzer electrically connected to the electromagnetic wave
transceiver, for analyzing the frequency of the electromagnetic
wave received from the electromagnetic wave transceiver; and a
computer electrically connected to the electromagnetic wave
generator and the frequency analyzer, for calculating a correlation
between the electron density and electron temperature, and a
corresponding electromagnetic wave based on a frequency band-based
transmission command of the electromagnetic wave and the analyzed
data, the method comprising: a first step of allowing the
electromagnetic wave generator to apply electromagnetic wave of a
predetermined frequency to the transmit antenna; a second step of
allowing the receive antenna to analyze a frequency of the
electromagnetic wave received from the transmit antenna; a third
step of measuring a cutoff frequency based on the analyzed
frequency; a fourth step of calculating an electron density of a
plasma using the measured cutoff frequency; a fifth step of
allowing the electromagnetic wave generator to transmit
electromagnetic wave, monitor reflected wave returned to the
transmit antenna, and measure a surface wave absorption frequency;
and a sixth step of calculating an electron temperature of the
plasma based on the electron density of the plasma and the
absorption frequency found in the fourth step and the fifth step,
respectively.
10. The method as claimed in claim 9, wherein the electron density
of the plasma in the fourth step is found according to the
following Equation 1, i.e., a relational expression of a plasma
frequency .omega..sub.pe (.i e., the cutoff frequency).
.omega..sub.pe=[n.sub.ee.sup.2/.epsilon..sub.0m.sub.e].sup.1/2
[Equation 1] where .omega..sub.pe is the plasma frequency, n.sub.e
is the electron density of the plasma, .epsilon..sub.0 is a
dielectric constant in the vacuum, and e and m.sub.e are an
electron charge and mass, respectively.
11. The method as claimed in claim 9, wherein the electron
temperature T.sub.e of the plasma in the sixth step is found
according to the following Equation 2 and Equation 3.
[1-[.omega..sub.pe/.omega.].sup.2]={K.sub.m(.beta.a)I.sub.m'(.beta.a)K.su-
b.m(.beta.b)-K.sub.m'(.beta.a)I.sub.m(.beta.b)}/{K.sub.m'(.beta.a)I.sub.m(-
.beta..sub.a)K.sub.m(.beta.b)-K.sub.m(.beta.a)I.sub.m(.beta.b)}
[Equation 2] where .omega. is the absorption frequency,
.omega..sub.pe is the plasma frequency, K.sub.m, I.sub.m, K.sub.m',
and I.sub.m' are modified Bessel functions, .beta.=2.pi./.lamda.,
.lamda.=2l, and l is the length of the transmit antenna, a is a
radius from the center of a metal unit of the transmit antenna to
the boundary of a sheath, and b is a radius of the metal unit of
the transmit antenna.
.lamda..sub.d=(.epsilon..sub.0T.sub.e/n.sub.ee.sup.2).sup.1/2
[Equation 3] s=n.lamda..sub.d where .lamda..sub.d is a Debye
length, T.sub.e is the electron temperature, n.sub.e is the
electron density of the plasma, .epsilon..sub.0 is the dielectric
constant in the vacuum, e is the electron charge, s is the width of
the sheath wherein s=a-b, and n is a given integer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates, in general, to a technique
that measures and monitors an electron density and an electron
temperature of a plasma by probing and scanning each
eigenfrequency, which is correlated to an electron density and
electron temperature of a plasma, in order to monitor a process
status using the plasma, such as a semiconductor fabrication
process. More particularly, the present invention relates to an
apparatus for monitoring an electron density and electron
temperature of a plasma, including a probe of an antenna structure
for transmitting/receiving a series of electromagnetic waves of a
band to/from a corresponding plasma and an analysis tool for
analyzing the bands of specific electromagnetic wave cutoff
frequency and absorption frequency of electromagnetic waves
transmitted, which are cut off or absorbed with respect to a
corresponding plasma, and calculating an electron density and
electron temperature of the corresponding plasma based on the
analysis result, and a method thereof.
[0003] 2. Background of the Related Art
[0004] In general, in the semiconductor fabrication process, plasma
has been widely used due to the necessity of the miniaturization
and low temperature of the process. Equipments used to fabricate
semiconductor devices include an ion implantation equipment for
implanting a desired impurity into a predetermined region of a
wafer, a furnace for growing a thermal oxide layer, a deposition
equipment for depositing a conduction layer or an insulating layer
on the wafer, exposure and etch equipments for patterning the
deposited conduction layer or the deposited insulating layer in a
desired form, and the like.
[0005] Of the equipments, a plasma equipment for forming plasma
within a sealed chamber of a vacuum state and implanting a reaction
gas to deposit or etch a material layer has been widely used as the
equipment for depositing a predetermined material layer on the
wafer or etching a predetermined material layer formed in the
wafer.
[0006] This is because if a material layer is deposited using
plasma, a process can be performed at low temperature, such as that
impurities within an impurity region formed in the wafer no longer
diffuse, and the regularity in the thickness of the material layer
formed in a wafer having a large diameter is good.
[0007] In a similar way, this is because if a predetermined
material layer formed on the wafer is etched using plasma, the etch
regularity is good over the entire waver.
[0008] In the plasma apparatus, tools capable of measuring an
electron density and an ion density within plasma include Langmuir
probe, a plasma oscillation probe, a plasma absorption probe, an
OES (Optical Emission Spectroscopy), a laser Thomson scattering
method, and so on.
[0009] The Langmuir probe of the tools is widely used. In the
conventional Langmuir probe, in order to measure the plasma
characteristic, the probe is inserted into plasma within a plasma
chamber from the outside, and voltages are varied from a negative
potential to a positive potential (i.e., in the range of -200V to
200V) and are measured by varying an externally supplied DC.
[0010] At this time, if a negative voltage is applied to the end of
the probe, positive ions within the plasma are absorbed by the
probe and a current is therefore generated due to the ions. If a
positive voltage is applied to the end of the probe, electrons
within the plasma are absorbed by the probe and a current is
therefore generated due to the electrons. In this case, the
concentration of the plasma can be measured by measuring the
generated current in order to analyze the correlation between the
generated current and the voltage applied to the probe.
[0011] In the conventional Langmuir probe, the plasma density can
be measured in real-time while the process is performed because the
plasma density is measured by inserting the probe into the chamber.
However, the conventional Langmuir probe has a noise problem due to
RF (Radio Frequency) oscillation, a problem in that a thin film
material is deposited on the probe at the time of depositing the
material in the semiconductor process, a problem in that the probe
becomes small due to etching at the time of a dry etch process, and
the like. This makes it impossible to apply the Langmuir probe to
an actual mass-production process.
[0012] Furthermore, the conventional plasma oscillation probe is
constructed to use an electron beam and employs a hot filament in
order to produce the electron beam. However, the plasma oscillation
probe is problematic in that it has a narrow operating condition,
such as that corresponding hot filament is broken at a pressure of
50 mT or more. The plasma oscillation probe is also problematic in
that the reaction container is polluted due to the evaporation of
hot filament upon heating in order to emit thermal electrons.
[0013] Furthermore, the conventional plasma absorption probe is
problematic in that correction must be carried out using an
accurate plasma density diagnosis tool before operation. A
structure for improving the problem has been proposed. However, the
proposed structure requires several steps of complicate calculation
processes for calculating an absolute value of a measurement
density. In this case, the proposed structure is problematic in
that the effectiveness is low since physically assumed conditions
are included.
[0014] In addition, the electron temperature measurement method
employing OES is problematic in that it is commercially applied
since sufficient data are not accumulated.
[0015] Finally, the laser Thomson scattering method is problematic
in that it is used only within a laboratory other than a
mass-production system because the size is very large and the
structure is very complicate.
[0016] Therefore, there is an urgent need for technology of a
device structure, which can overcome the conventional problems, can
measure an electron density and electron temperature of a plasma
more rapidly and accurately, can monitor a process thereof in
real-time, and can be applied to the mass-production system with
less limitations.
SUMMARY OF THE INVENTION
[0017] Accordingly, the present invention has been made in view of
the above problems occurring in the prior art, and it is a first
object of the present invention to provide an apparatus for
monitoring an electron density and electron temperature of a
plasma, including an electromagnetic wave transceiver of an antenna
structure, which can transmit/receive electromagnetic waves of a
series of bands so that a frequency band that is correlated to an
electron density and electron temperature can be measured/monitored
in real-time.
[0018] It is a second object of the present invention to provide an
apparatus for monitoring an electron density and electron
temperature of a plasma, including a frequency analyzer for
analyzing a cutoff frequency and an absorption frequency that are
correlated to a corresponding electron density and electron
temperature based on a frequency band of received electromagnetic
wave.
[0019] It is a third object of the present invention to provide an
apparatus for monitoring an electron density and electron
temperature of a plasma, including a conveyer for conveying an
electromagnetic wave transceiver within a reaction container such
that spatial distributions can be measured by measuring the
electron density and electron temperature of the plasma on a
position basis within a plasma reaction container.
[0020] To achieve the above objects, according to an aspect of the
present invention, there is provided an apparatus for monitoring an
electron density and electron temperature of a plasma, including an
electromagnetic wave generator that continuously transmits
electromagnetic wave of a series of frequency bands, an
electromagnetic wave transceiver connected to a plasma within a
reaction container and electrically connected to the
electromagnetic wave generator so that a frequency of the
transmitted electromagnetic wave is correlated to the electron
density and electron temperature of the plasma, the electromagnetic
wave transceiver transmitting the electromagnetic wave, a frequency
analyzer electrically connected to the electromagnetic wave
transceiver, for analyzing the frequency of the electromagnetic
wave received from the electromagnetic wave transceiver, and a
computer electrically connected to the electromagnetic wave
generator and the frequency analyzer, for calculating a correlation
between the electron density and electron temperature, and a
corresponding electromagnetic wave based on a frequency band-based
transmission command of the electromagnetic wave and the analyzed
data.
[0021] The electromagnetic wave transceiver may include first and
second coaxial cables that are electrically connected to the
electromagnetic wave generator and the frequency analyzer,
respectively, and are disposed in parallel, and a transmit antenna
and a receive antenna that are connected to and projected from one
ends of the first and second coaxial cables, respectively, on the
same axial line and are connected to the plasma in order to
transmit and receive the electromagnetic wave.
[0022] Each of the first and second coaxial cables may include a
dielectric-coated layer coated/shielded at a predetermined
thickness.
[0023] Furthermore, the apparatus may further include a conveyer
connected to the other end of the electromagnetic wave transceiver,
for causing the electromagnetic wave transceiver to be selectively
conveyed within the reaction container.
[0024] The conveyer may be driven by a stepping motor.
[0025] Alternatively, the conveyer may be driven by an oil-pressure
cylinder.
[0026] It is preferred that the electromagnetic wave transceiver is
disposed along a radial direction of the reaction container in
obtaining characteristic distributions of the plasma within the
reaction container.
[0027] Further objects, specific merits and novel characteristics
of the invention will become more apparent from the following
detailed description and exemplary embodiments taken in conjunction
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Further objects and advantages of the invention can be more
fully understood from the following detailed description taken in
conjunction with the accompanying drawings in which:
[0029] FIG. 1 shows the construction of an apparatus for monitoring
an electron density and electron temperature of a plasma according
to an embodiment of the present invention;
[0030] FIG. 2 is a cross-sectional view of transmit/receive
antennas shown in FIG. 1;
[0031] FIG. 3 is a view illustrating convey within a reaction
container of an electromagnetic wave transceiver shown in FIG.
1;
[0032] FIG. 4a is a graph illustrating cutoff frequencies measured
using the monitoring apparatus according to an embodiment of the
present invention;
[0033] FIG. 4b is a graph illustrating absorption frequencies
measured using the monitoring apparatus according to an embodiment
of the present invention;
[0034] FIG. 5 is a graph illustrating electron density and electron
temperature measured using the monitoring apparatus according to an
embodiment of the present invention; and
[0035] FIG. 6 is a flowchart illustrating a method of measuring an
electron temperature of a plasma according to an embodiment of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0036] An apparatus for monitoring an electron density and electron
temperature of a plasma according to an embodiment of the present
invention will now be described in detail with reference to the
accompanying drawings.
[0037] FIG. 1 shows the construction of an apparatus for monitoring
an electron density and electron temperature of a plasma according
to an embodiment of the present invention. FIG. 2 is a
cross-sectional view of transmit/receive antennas shown in FIG.
1.
[0038] Referring to FIGS. 1 and 2, the monitoring apparatus
according to the present invention is adapted to measure a
corresponding characteristic value and monitor the characteristic
value in real-time, by finding a correlation between the
characteristics of electromagnetic wave and a plasma 100a (more
particularly, an electron density, an electron temperature, and so
on) and monitoring.
[0039] In order to have the correlation, the monitoring apparatus
of the present invention includes an electromagnetic wave
transceiver 200 for transmitting/receiving electromagnetic wave
to/from the plasma 100a. For the purpose of such
transmission/reception, the electromagnetic wave transceiver 200
has an antenna structure.
[0040] What is contained in a cylindrical reaction container 100 is
the plasma 100a. It has been known that if electromagnetic wave of
a specific band is transmitted to the plasma 100a, corresponding
electromagnetic wave is cut off or absorbed. A specific
electromagnetic wave of a frequency band that is cut off or
absorbed as described above becomes the index of an electron
density or an electron temperature of the plasma 100a. It is
therefore possible to obtain an electron density and electron
temperature of the plasma 100a based on a correlation between the
electromagnetic wave and the plasma 100a.
[0041] The correlation is established in the electromagnetic wave
transceiver 200. An electromagnetic wave generator 300 and the
frequency analyzer 400 are electrically connected to the
electromagnetic wave transceiver 200 in order to transmit
electromagnetic wave to the electromagnetic wave transceiver 200 or
to analyze received electromagnetic wave.
[0042] In this case, the electromagnetic wave transceiver 200
includes two coaxial cables 210, 220 that are disposed in parallel.
Each of the coaxial cables 210, 220 is surrounded with an
additional dielectric-coated layer 230 and a ground shield, for
preventing the coaxial cables 210, 220 from noise, heat, etc.
Accordingly, electromagnetic wave can be transmitted and received
more accurately. The dielectric-coated layer 230 may be formed of
alumina or quartz.
[0043] Furthermore, transmit/receive antennas 210a, 220b are
connected to and projected from one ends of the coaxial cables 210,
220, respectively, on the same axial line, and transmit/receive
electromagnetic wave to/from the plasma 100a.
[0044] Referring to FIG. 2, if the metal antennas 210a, 220a having
a radius "b" are inserted into the plasma, a sheath 240 having a
thickness "s" is formed on an outer surface of the antenna, thus
surrounding the circumference of the antenna. In the present
embodiment, the antennas 210a, 220a may be disposed at a distance
of about 1 mm to 5 mm and may have a length of about 5 mm to 10 mm.
The distance is only illustrative. The smaller the distance, the
better. In addition, the length of each of the antennas 210a, 220a
may be varied depending on a wavelength of electromagnetic wave
used.
[0045] The electromagnetic wave generator 300 is connected to the
other end of the first coaxial cable 210 and consecutively
transmits electromagnetic waves of a frequency band of about 50 kHz
to 10 GHz to the first coaxial cable 210 and the transmit antenna
210a. Consequently, a series of electromagnetic waves of a
frequency band can be transmitted to the plasma 100a
consecutively.
[0046] In this case, the cutoff frequency of the transmitted
electromagnetic waves is cut off with respect to the plasma 100a.
The cutoff frequency can be used to calculate and obtain an
electron density of a corresponding plasma 100a. Furthermore, an
electromagnetic wave of a band absorbed by the plasma 100a is an
absorption electromagnetic wave, which can be used to calculate and
obtain an electron temperature of a corresponding plasma 100a.
[0047] The frequency analyzer 400 is also connected to the other
end of the second coaxial cable 220. The frequency analyzer 400
serves to analyze an amplitude from a frequency of electromagnetic
wave, which is received and obtained by the receive antenna 220a
and the second coaxial cable 220.
[0048] If the transmitted electromagnetic wave is cut off, however,
the receive rate of the electromagnetic wave in the receive antenna
220a is very weak. Accordingly, the electromagnetic wave of the
weakest receive rate can be analyzed as the cutoff frequency. The
frequency analyzer 400 can identify the weakest frequency by
analyzing a frequency, an amplitude, and so on of the obtained
electromagnetic wave. It is therefore possible to analyze/obtain
the cutoff frequency.
[0049] Furthermore, if there is electromagnetic wave absorbed by
the plasma 100a, the electromagnetic wave is weakly reflected from
the transmit antenna 220a and the first coaxial cable 220. It
causes to generate resonance in the sheath space between the plasma
100a and the transmit antenna 220a by way of a kind of a cavity,
resulting in a strong absorption of the electromagnetic wave.
Therefore, a signal of the reflected electromagnetic wave becomes
the weakest. That is, it is meant that a ratio in which the
electromagnetic wave is reflected from the transmit antenna again
is low. It is possible to obtain/acquire a corresponding frequency
band of the absorbed electromagnetic wave by analyzing a frequency
band, amplitude, etc. of the weakly reflected electromagnetic wave.
Accordingly, there is provided a structure capable of
analyzing/acquiring an absorption frequency band.
[0050] A computer 500 is provided to calculate an electron density
and an electron temperature based on the occurrence of a series of
the electromagnetic waves, a received command, and analyzed
frequency data. The computer 500 is electrically connected the
electromagnetic wave generator 300 and the frequency analyzer
400.
[0051] Therefore, if the electromagnetic wave transceiver 200 is
connected to the plasma 100a within the reaction container 100 and
transmits electromagnetic wave, a frequency band, etc. is obtained
from a weakly received electromagnetic wave and data of a cutoff
frequency and an absorption frequency are transmitted to the
computer 500. Calculation equations capable of calculating an
electron density and/or an electron temperature based on a
frequency are programmed into the computer 500. Accordingly, a
structure that can calculate and acquire an electron density and
electron temperature of a corresponding plasma 100a can be
provided.
[0052] FIG. 3 is a view illustrating convey within the reaction
container 100 of the electromagnetic wave transceiver 200 shown in
FIG. 1.
[0053] As shown in FIG. 3, the monitoring apparatus according to
the present invention includes a conveyer 600. To the other end of
the electromagnetic wave transceiver 200 is connected the conveyer
600.
[0054] In the present invention, the conveyer 600 may have a power
structure that allows for a straight-line convey, such as a
stepping motor structure or an oil-pressure cylinder structure. The
conveyer 600 is constructed to convey the electromagnetic wave
transceiver 200, which is disposed to move along a radial direction
within the cylindrical reaction container 100, in a straight line
forward and backward.
[0055] As described above, the conveyer 600 is constructed to
convey the electromagnetic wave transceiver 200 in the straight
line. Therefore, the electromagnetic wave transceiver 200 can
transmit/receive electromagnetic wave while moving in the straight
line within the plasma 100a. Furthermore, there is provided a
structure capable of analyzing, measuring, and monitoring spatial
distributions of an electron density and electron temperature of a
corresponding plasma 100a.
[0056] FIG. 4a is a graph illustrating cutoff frequencies measured
using the monitoring apparatus according to an embodiment of the
present invention, and FIG. 4b is a graph illustrating absorption
frequencies measured using the monitoring apparatus according to an
embodiment of the present invention.
[0057] Referring to FIG. 4a, the X axis denotes a frequency band
(Hz) and the Y axis denotes an amplitude of electromagnetic wave
(au.), which is received by the receive antenna 220a. From FIG. 4a,
it can be seen that as the frequency increases, the amplitude
increases, then decreases at about 1.5.times.10.sup.9 Hz, and then
becomes the lowest at a frequency of about 2.5.times.10.sup.9 Hz
(indicated by an arrow in the drawing). A portion indicating the
lowest amplitude, of ones in which the electromagnetic wave
received as described above is indicated as the frequency band
versus the amplitude, is the cutoff frequency.
[0058] The cutoff frequency is a frequency of a band that does not
transmit the plasma 100a when the transmit antenna 210a transmits
the electromagnetic wave to the plasma 100a as mentioned earlier.
Accordingly, a very weak signal is received by the receive antenna
220a. The cutoff frequency serves as an index to detect an electron
density of the plasma 100a.
[0059] In the present embodiment, the electromagnetic wave
generator 300 generates electromagnetic waves. The generated
electromagnetic waves are consecutively transmitted to the transmit
antenna 210a through the first coaxial cable 210 on a frequency
basis and are then transmitted to the plasma 100a.
[0060] The electromagnetic waves that have been transmitted and
have been cut off and weaken in the plasma 100a as described above
are continuously received by the receive antenna 220a. The
electromagnetic waves are then transmitted to the frequency
analyzer 400 connected to the second coaxial cable 220 and are then
analyzed on a frequency-band basis.
[0061] The analyzed data are transmitted to the computer 500 and
are then indicated as the graph as shown in FIG. 4a. Furthermore,
what is indicated as a frequency band of the lowest amplitude in
the graph is the cutoff frequency. Therefore, there is provided a
structure in which the computer 500 can calculate/acquire an
electron density of a corresponding plasma 100a based on the cutoff
frequency acquired through the above operation.
[0062] In addition, referring to FIG. 4b, an X axis denotes a
frequency band (Hz) and a Y axis denotes a predetermined reflection
coefficient (dB). Accordingly, in the case where electromagnetic
waves are transmitted to a corresponding plasma 100a, an absorption
frequency can be acquired by analyzing electromagnetic wave of a
corresponding frequency having the lowest reflection coefficient
through a process in which the electromagnetic wave is reflected
and received.
[0063] Analyzed data of the absorption frequency obtained as
described above are transmitted to the computer 500. Accordingly,
there is provided a structure in which the computer 500 can measure
an electron temperature of a corresponding plasma 100a based on the
analyzed data.
[0064] FIG. 5 is a graph illustrating electron density and electron
temperature measured using the monitoring apparatus according to an
embodiment of the present invention.
[0065] Referring to FIG. 5, an X axis denotes a pressure (mTorr) of
the plasma 100a within the reaction container 100, and a Y axis on
the right side denotes an electron density (cm.sup.-3) of the
plasma 100a on a pressure basis and a Y axis on the left side
denotes an electron temperature (eV) of the plasma 100a on a
pressure basis.
[0066] From FIG. 5, it can be seen that in the case where argon
(Ar) plasma is used in the present invention, the electron density
of the plasma 100a increases as the gas pressure increases, but the
electron temperature of the plasma 100a decreases as the discharge
gas pressure increases.
[0067] Therefore, FIG. 5 shows that the slope of the graph of the
electron density indicated by a straight line and triangles is
opposite to the slope of the graph of the electron temperature
indicated by a straight line and squares.
[0068] It has been illustrated above that the apparatus for
monitoring an electron density and electron temperature of a plasma
according to an embodiment of the present invention has a structure
in which one electromagnetic wave transceiver 200 in which the
conveyer 600 is connected to one end of the reaction container 100
is mounted. However, the present invention can be applied to a
structure in which respective electromagnetic wave transceivers 200
are mounted in the other side, and upper and lower sides of the
reaction container 100, and the conveyers 600 are connected to the
respective electromagnetic wave transceivers 200 and measure
three-dimensional spatial distributions of an electron density and
electron temperature of the X-Y-Z axis while moving within the
reaction container 100 in the respective axial directions.
[0069] Furthermore, the transmit antenna 210a and the receive
antenna 220a of the straight-line type have been illustrated above
as means for transmitting and receiving electromagnetic wave. It is
however to be noted that a loop antenna, a superturnstile antenna,
an excitation antenna, a parabola antenna or the like may be
selectively used as the means for transmitting and receiving
electromagnetic wave.
[0070] FIG. 6 is a flowchart illustrating a method of measuring an
electron temperature of a plasma according to an embodiment of the
present invention.
[0071] Referring to FIG. 6, a method of monitoring an electron
temperature using the electron temperature monitoring apparatus of
the present invention includes a first step (S1) of allowing the
electromagnetic wave generator 300 to apply electromagnetic wave of
a predetermined frequency to the transmit antenna 210a, a second
step (S2) of allowing the receive antenna 220a to analyze a
frequency of the electromagnetic wave received from the transmit
antenna 210a, a third step (S3) of measuring a cutoff frequency
based on the analyzed frequency, a fourth step (S4) of calculating
an electron density of a plasma using the measured cutoff
frequency, a fifth step (S5) of allowing the electromagnetic wave
generator 300 to transmit electromagnetic wave, monitor reflected
wave returned to the transmit antenna 210a, and measure a surface
wave absorption frequency, and a sixth step (S6) of calculating an
electron temperature based on the plasma density and the absorption
frequency found in the fourth step (S4) and the fifth step (S5),
respectively.
[0072] In the case of a process employing common plasma, the plasma
itself includes a unique plasma frequency whose state is changed.
The plasma frequency is directly related to the plasma density.
Therefore, the electron density of the plasma can be measured
directly by measuring the plasma frequency.
[0073] In the event that a frequency of common electromagnetic wave
corresponds to the plasma frequency, the frequency has a property
that if the electromagnetic wave is incident on the plasma, it is
cut off and does not transmit the plasma. Therefore, if the
electromagnetic wave generating apparatus transmits a frequency of
50 kHz to 10 GHz to the transmit antenna, the electromagnetic wave
output from the transmit antenna can be received by the receive
antenna.
[0074] At this time, electromagnetic wave having the plasma
frequency decided according to the plasma density does not pass
through the plasma. Accordingly, the electromagnetic wave is not
received by the receive antenna or only a very weak signal is
received by the receive antenna.
[0075] That is, as shown in FIG. 4a, the cutoff frequency of the
lowest value can be found from the frequency spectrum through the
frequency analyzer 400. The cutoff frequency is a plasma frequency
(.omega..sub.pe). The electron density of the plasma can be found
based on the plasma frequency (.omega..sub.pe) in accordance with
the following Equation 1.
.mu..sub.p2=[n.sub.ee.sup.2/.epsilon..sub.0m.sub.e].sup.1/2
[Equation 1]
[0076] where .omega..sub.pe is the plasma frequency, n.sub.e is the
electron density of the plasma, .epsilon..sub.0 is the dielectric
constant in the vacuum, and e and m.sub.e are the electron charge
and mass, respectively.
[0077] Meanwhile, if the electromagnetic wave generator 300
transmits electromagnetic wave and the transmit antenna 210a
monitors returned reflected wave, a surface wave absorption
frequency of the transmit antenna 210a can be measured.
[0078] In other words, the spectrum of the electromagnetic wave
reflected from the transmit antenna 210a of FIG. 1 is shown in FIG.
4b. A dispersion equation of the surface wave can be expressed in
the following Equation 2.
[1-[.omega..sub.pe/.omega.].sup.2]={K.sub.m(.beta.a)I.sub.m'(.beta.a)K.s-
ub.m(.beta.b)-K.sub.m'(.beta.a)I.sub.m(.beta.b)}/{K.sub.m'(.beta.a)I.sub.m-
'(.beta.a)I.sub.m(.beta.a)K.sub.m(.beta.b)-K.sub.m(.beta.a)I.sub.m(.beta.b-
)} [Equation 2]
[0079] where .omega. is the absorption frequency, .omega..sub.pe is
the plasma frequency, K.sub.m, I.sub.m, K.sub.m', and I.sub.m' are
modified Bessel functions, .beta.=2.pi./.lamda., .lamda.=2l, and l
is the length of the transmit antenna, a is the radius from the
center of a metal unit of the transmit antenna to the boundary of
the sheath, and b is the radius of the metal unit of the transmit
antenna.
[0080] Furthermore, an electron temperature T.sub.e can be found
using the surface wave dispersion equation of the above-mentioned
Equation 2, a Debye length .lamda..sub.d defined by the following
Equation 3, and the width s of the sheath. FIG. 2 shows the
relationship between the sheath width s of the transmit antenna,
and "a" and "b".
.lamda..sub.d=(.epsilon..sub.0T.sub.w/n.sub.ee.sup.2).sup.1/2
[Equation 3]
s=n.lamda..sub.d
[0081] where .lamda..sub.d is the Debye length, T.sub.e is the
electron temperature of the plasma, n.sub.e is the electron density
of the plasma, .epsilon..sub.0 is the dielectric constant in the
vacuum, e is the electron charge, s is the width of the sheath
wherein s=a-b, and n is a given integer.
[0082] Therefore, the cutoff frequency is the plasma frequency
.omega..sub.pe and other parameters are constants corresponding to
a structural antenna size. Accordingly, the electron temperature
T.sub.e can be found by measuring the absorption frequency
.omega..
[0083] In accordance with an apparatus and method for monitoring an
electron density and electron temperature of a plasma according to
the present invention, an electron density and electron temperature
of a plasma can be measured by detecting an eigenfrequency.
Therefore, the present invention is advantageous in that it can be
applied to a thin film plasma chemical deposition method of a
semiconductor fabrication process, a plasma process apparatus in a
dry etch process, and so on.
[0084] Furthermore, the apparatus of the present invention can be
used as a plasma real-time monitoring apparatus. Therefore, there
is an advantage in that the apparatus of the present invention can
be utilized as a reliable process equipment since it can check a
current status of a process equipment.
[0085] While the present invention has been described with
reference to the particular illustrative embodiments, it is not to
be restricted by the embodiments but only by the appended claims.
It is to be appreciated that those skilled in the art can change or
modify the embodiments without departing from the scope and spirit
of the present invention.
* * * * *